#include <iostream>
 
#define maxn 5000010

int n, k;
int A[maxn], Deque[maxn];
int Front, Back;
long long Sum;
 
int main() {
	freopen("deque.in", "r", stdin);
	freopen("deque.out", "w", stdout);
 
	cin >> n >> k;
 
	for (int i = 1; i <= n; i++) 
		cin >> A[i];
 
	Front = 1, Back = 0;
 
	for (int i = 1; i <= n; i++) {
		while (Front <= Back && A[i] <= A[ Deque[Back] ]) Back--;		
		Deque[++Back] = i;
 
		if (Deque[Front] == i-k) Front++;
 
		if (i >= k) Sum += A[ Deque[Front]]; 	
	}
 
	cout << Sum;
 
	return 0;
}